Liquid crystal display apparatus

ABSTRACT

The invention discloses a liquid crystal display apparatus and a pixel element design thereof. The liquid crystal display apparatus includes a register, a liquid crystal display panel, a driving circuit, a dynamic frequency adjustment unit and a control circuit. The liquid crystal display panel includes a plurality of liquid crystal capacitors and a plurality of pixel units. The driving circuit includes a plurality of storage capacitors corresponding to the liquid crystal capacitors. A capacitance of the storage capacitors far exceeds a capacitance of the liquid crystal capacitors. The driving circuit casts the image information on the liquid crystal display panel. The dynamic frequency adjustment unit computes and judges based on an image characteristic classification of the image information, so as to generate a display mode control signal dynamically.

RELATED APPLICATIONS

This application is a Divisional Application based on U.S. applicationSer. No. 13/338,250, filed Dec. 28, 2011, and also claims the benefit ofTaiwanese Application Serial Number 099147378, filed Dec. 31, 2010, thedisclosures of both of which are hereby incorporated by reference hereinin their entirely.

BACKGROUND

1. Field of Invention

The invention relates to a liquid crystal display apparatus. Moreparticularly, the invention relates to a pixel element design and amethod for driving the liquid crystal display apparatus.

2. Description of Related Art

In recent years, a liquid crystal display (LCD) apparatus has beenapplied in many areas, including a notebook personal computer, amonitor, a vehicular navigation device, a functional calculator, varioussizes of TV sets, a mobile phone and an electronic message board.Particularly, the current thin and light or portable electronic productshave become a new trend in the market. The LCD apparatus has a smallervolume and thickness than the prior CRT (cathode-ray tube) displayapparatus, so the LCD apparatus has been widely applied.

In the development of the current electronic display technology, thepower consumption of the display apparatus is emphasized, so the LCDapparatus with low power consumption better meets the requirements of auser for energy saving and environment protection. Particularly, in aportable display apparatus (such as a cellular phone, a smart phone, aPDA (personal digital assistant), an e-book and a tablet computer), thepower consumption of the LCD module directly influences the endurance ofthe entire apparatus. Particularly, in the current large-size, thin andlight display apparatus, the LCD module with the low power consumptionand high efficiency is urgently demanded.

The current LCD apparatus generally has a certain refresh rate or framerate. Generally, the LCD apparatus adopts the rate of 50-70 Hz. That is,the frame refreshes 50-70 times per second.

In other words, even if the display frame of the LCD apparatus has nochange or few changes, the display driving circuit may stillperiodically refresh a display signal of each pixel of the displaymodule at the rate of 60 times per second. Thus, unnecessary energyconsumption is generated.

For a current general TFT-LCD (thin film transistor liquid crystaldisplay) apparatus on the market, the power consumption is mainly causedby the LCD panel, the driving circuit and the backlight module. Takingthe 10.1-inch TFT-LCD apparatus as an example, the power consumption ofthe LCD panel and the driving circuit is approximately between 1000 mWand 2000 mW. On the other hand, the power consumption of the backlightmodule is approximately between 2000 mW and 3000 mW.

Although a polarity inversion driving method, e.g. a row inversiondriving method or a frame inversion driving method, has been proposed inthis industry directed for the driving circuit, and an area scanningbacklight method has been proposed directed for the backlight module,the above methods have limited effects. Therefore, those in the industryare endeavoring to find an LCD apparatus having a stable display effectand low energy consumption and a display driving method thereof.

SUMMARY

In order to solve the problems above, the invention discloses a liquidcrystal display apparatus having a dynamic adjustable refresh rate, anda liquid crystal display apparatus driven by a low refresh rate throughthe design of a pixel element and a storage capacitor in a (multi)dual-TFT driving circuit and the liquid crystal material thereof. In theliquid crystal display apparatus having the dynamic adjustable refreshrate of the invention, the liquid crystal display apparatus cancorrespondingly adjust the display refresh rate of the driving circuitbased on an image characteristic classification (such as a dynamicstate, a static state, images, texts, fast changing and slow changing)of the currently displayed image information, thereby achieving thepower saving effect by adopting a low display refresh rate. The dynamicfrequency adjustment unit at least has two or more sets of frame rates.

At a low display refresh rate, the potential of a storage capacitor in ageneral liquid crystal display apparatus gradually changes with time,which causes the transmittance of the liquid crystal display panelchanges accordingly. For example, the transmittance under a normallywhite mode increases with time, and the transmittance under a normallyblack mode decreases with time, which may lead to an uneven displaybrightness or luminance in a display frame cycle, thereby furthercausing phenomena of scintillation and screen flicker. This problem canbe solved by, for example, periodically adjusting the driveconfiguration of a backlight module in a display frame cycle through aliquid crystal display apparatus having brightness or luminance holdingratio compensation.

Accordingly, an aspect of the invention provides a liquid crystaldisplay apparatus, which includes a register, a liquid crystal displaypanel, a driving circuit, a dynamic frequency adjustment unit and acontrol circuit. The register is used for temporarily storing imageinformation. The liquid crystal display panel includes a plurality ofliquid crystal capacitors. The driving circuit includes a plurality ofstorage capacitors corresponding to the liquid crystal capacitors. Acapacitance of the storage capacitors far exceeds a capacitance of theliquid crystal capacitors. The driving circuit casts the imageinformation on the liquid crystal display panel. The dynamic frequencyadjustment unit dynamically generates a display mode control signalbased on an image characteristic classification of the imageinformation. The control circuit is electrically connected with thedynamic frequency adjustment unit and the driving circuit. The controlcircuit accordingly adjusts the display refresh rate and driveparameters of the driving circuit according to the display mode controlsignal.

According to an embodiment of another aspect of the invention, thedriving circuit includes at least two thin film transistor switchescorresponding to each pixel unit. An off-state leakage current of thedriving circuit is less than or equal to 10⁻¹² ampere. In thisembodiment, the at least two thin film transistor switches form adual-gate thin film transistor (TFT). In another embodiment, anoff-state leakage current of the driving circuit may be further lessthan or equal to 10⁻¹³ ampere.

According to another embodiment of the invention, the driving circuitincludes a lightly doped drain (LDD) TFT. The TFT at least has a firstLDD and a second LDD with different lengths. The first LDD nearest tothe driving transistor has the largest length, and an off-state leakagecurrent of the driving circuit is less than or equal to 10⁻¹² ampere. Inthis embodiment, an off-state leakage current of the driving circuit maybe further less than or equal to 10⁻¹³ ampere.

According to yet another embodiment of the invention, the drivingcircuit adopts a dual-gate TFT driving architecture. An off-stateleakage current of the driving circuit is less than 10⁻¹³ ampere.

According to another embodiment of the invention, an average capacitanceof the liquid crystal capacitors is larger than or equal to 0.5picofarad, and the capacitance of the storage capacitors is larger thanor equal to ten times of that of the liquid crystal capacitors.

According to still another embodiment of the invention, the capacitanceof the storage capacitors is larger than or equal to fifty times of thatof the liquid crystal capacitors.

According to still yet another embodiment of the invention, the liquidcrystal impedance is larger than or equal to 10¹³ ohm/cm, and analignment-film impedance of the liquid crystal display panel is largerthan or equal to ten times of the liquid crystal impedance.

According to an embodiment of the invention, an alignment-film impedanceof the liquid crystal display panel is further larger than or equal tofifty times of the liquid crystal impedance.

According to another embodiment of the invention, the liquid crystaldisplay panel includes a plurality of pixel units respectivelycorresponding to the storage capacitors. The area ratio of the storagecapacitors to the pixel units is larger than or equal to 85%.

According to yet another embodiment of the invention, in a method fordriving the liquid crystal display panel, row inversion or frameinversion is used for driving the display panel.

According to still another embodiment of the invention, the imagecharacteristic classification at least includes a dynamic image, astatic slow image or a static holding image.

According to still yet another embodiment of the invention, the imageinformation further has an image characteristic sub-classification. Theimage characteristic sub-classification at least includes a full colormode, an image mode, a text mode and/or a monochromatic system. Thedynamic frequency adjustment unit generates a corresponding display modecontrol signal based on the image characteristic classification and theimage characteristic sub-classification of the image information.

According to an embodiment of the invention, the dynamic frequencyadjustment unit at least has two or more sets of refresh rates.

According to another embodiment of the invention, the displayconfiguration at least includes a gray level.

According to yet another embodiment of the invention, the dynamicfrequency adjustment unit at least has a frame rate lower than 20 Hz. Instill another embodiment, the dynamic frequency adjustment unit at leasthas a frame rate lower than 5 Hz.

According to still yet another embodiment of the invention, the liquidcrystal display panel includes a plurality of pixel units. Each pixelunit at least corresponds to one of the liquid crystal capacitors andone of the storage capacitors. Each pixel includes a first electrodelayer (M1), an extension layer (M2) of a source layer and a drain layerof a second electrode layer, and a pixel electrode layer (M3) of a thirdelectrode layer sequentially disposed on a lower substrate, and adielectric layer material is respectively disposed therebetween. Thefirst electrode layer includes a gate layer and/or a common electrodeconductive layer. The extension layer of the drain layer of the secondelectrode layer is connected with the pixel electrode layer, and/or thecommon electrode conductive layer of the first electrode layer iselectrically connected with a common transparent electrode layer of theupper substrate. The liquid crystal capacitor is formed between thecommon transparent electrode layers (ITO, IZO) of the upper substrateand the pixel electrode layer of the lower substrate. On the lowersubstrate, the storage capacitor is disposed between the commonelectrode conductive layer of the first electrode layer and theextension layer of the second electrode layer, and/or between the commonelectrode conductive layer of the first electrode layer and the pixelelectrode layer, and/or between the gate layer of the first electrodelayer and the pixel electrode layer.

In an embodiment, the pixel electrode layer may be of the pixelelectrode layer architecture including Indium Tin Oxide (ITO) slits, andthe liquid crystal layer is constructed by negative liquid crystalsaligned vertically.

In this embodiment, the pixel electrode layer is a transparentelectrode, a metal reflective electrode or a combination thereof. Theliquid crystal display panel is a transmissive liquid crystal displaypanel, a reflective liquid crystal display panel, a transflective liquidcrystal display panel or a partially reflective liquid crystal displaypanel.

According to another embodiment of the invention, the liquid crystaldisplay panel includes a plurality of pixel units. Each pixel unit atleast corresponds to one of the liquid crystal capacitors and one of thestorage capacitors. Each pixel includes a gate layer (M1) of a firstelectrode layer, a second electrode layer (M2), and a common electrodelayer (M3) of a third electrode layer sequentially disposed on the lowersubstrate, and a dielectric layer material is respectively disposedtherebetween.

The second electrode layer includes a source layer, a drain layer, and apixel electrode layer connected with the drain layer. The pixelelectrode layer of the second electrode layer and the common electrodelayer of the third electrode layer are formed in a comb-shaped electrodearchitecture, a grid-shaped electrode architecture, a curvingcomb-shaped electrode architecture or a curving grid-shaped electrodearchitecture. No common electrode layer is disposed on the uppersubstrate. The liquid crystal capacitor is formed in the curvingelectric field between the pixel electrode layer of the second electrodelayer and the common electrode layer of the third electrode layer. Onthe lower substrate, the storage capacitor is disposed between the pixelelectrode layer of the second electrode layer and the common electrodelayer of the third electrode layer.

In another embodiment, the lower substrate of the liquid crystal displayapparatus at least includes a pixel electrode layer and a commonelectrode layer, and an insulation layer is disposed therebetween forisolation. The pixel electrode layer and the common electrode layer maybe formed in a comb-shaped electrode architecture, a grid-shapedelectrode architecture, a curving comb-shaped electrode architecture ora curving grid-shaped electrode architecture, such as an in planeswitching architecture. The liquid crystal molecular layer may bepositive or negative liquid crystals aligned horizontally. The pixelelectrode layer and the common electrode layer are metal or alloyconductive electrodes.

In yet another embodiment, the liquid crystal display apparatus of thein plane switching architecture at least includes a pixel electrodelayer and a common electrode layer. The pixel electrode layer and thecommon electrode layer may be formed in a comb-shaped electrodearchitecture, a grid-shaped electrode architecture, a curvingcomb-shaped electrode architecture or a curving grid-shaped electrodearchitecture. The common electrode layer is a first metal electrode M1,and the pixel electrode layer is a second metal electrode M2. Thestorage capacitor formed by the M1 and M2 may be located at the positionof the comb-shaped or grid-shaped electrodes, and even a comb-shaped orgrid-shaped storage capacitor, or a circumambient or circle (orsquare-shaped) storage capacitor is formed.

In still another embodiment, the lower substrate of the liquid crystaldisplay apparatus at least includes a pixel electrode layer and a commonelectrode layer, and an insulation layer is disposed therebetween forisolation. The pixel electrode layer may be of a fringe field switchingarchitecture. The liquid crystal molecular layer may be constructed bynegative liquid crystals aligned horizontally. The pixel electrode layerand the common electrode layer are ITO or IZO transparent electrodes, ormetal or alloy conductive electrodes. The pixel electrode layer of thefringe field switching architecture may be a rectangle or unit-pixelelectrode, a comb-shaped or grid-shaped electrode, or a curvingcomb-shaped or grid-shaped electrode. The common electrode layer may bea comb-shaped or grid-shaped electrode, or a curving comb-shaped orgrid-shaped electrode.

In this embodiment, the dielectric layer material is a silica materialSiOx, a nitrogen oxide material SiNx, a resin material, a plasticmaterial or a photoresist material. In this embodiment, on the uppersubstrate, an interval between the common electrode layer and the drainlayer is less than or equal to 0.2 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to make the following as well as other aspects, features,advantages, and embodiments of the invention more apparent, theaccompanying drawings are described as follows:

FIG. 1 illustrates a functional block diagram of a liquid crystaldisplay apparatus according to a first specific embodiment of theinvention;

FIG. 2 illustrates a schematic circuit diagram of a liquid crystaldisplay apparatus;

FIG. 3 illustrates a schematic top view of a pixel unit of the liquidcrystal display apparatus;

FIG. 4 illustrates a schematic sectional view of the liquid crystaldisplay panel and the driving circuit of the liquid crystal displayapparatus;

FIG. 5 illustrates a schematic view of a storage capacitor of a pixelunit;

FIG. 6 illustrates a schematic view of a dual-gate architecture;

FIG. 7 illustrates a schematic view of another dual-gate architecture;

FIG. 8 illustrates a schematic top view of a pixel unit of a liquidcrystal display apparatus according to a second specific embodiment ofthe invention;

FIG. 9 illustrates a schematic sectional view of the pixel unitaccording to the second specific embodiment of the invention;

FIG. 10 illustrates a schematic view of a pixel unit of an in planeswitching architecture;

FIG. 11 illustrates a schematic view of a pixel unit of an in planeswitching architecture;

FIG. 12 illustrates a schematic view of a pixel unit of an fringe fieldswitching architecture;

FIG. 13 illustrates a schematic view of a pixel unit of an fringe fieldswitching architecture; and

FIG. 14 illustrates a schematic view of a pixel electrode layer havingITO slits.

DETAILED DESCRIPTION

Referring to FIG. 1, FIG. 1 illustrates a functional block diagram of aliquid crystal display apparatus 100 according to a first specificembodiment of the invention. As shown in FIG. 1, the liquid crystaldisplay apparatus 100 includes a register 102, a dynamic frequencyadjustment unit 104, a liquid crystal display panel 120, a drivingcircuit 140 and a control circuit 160.

The register 102 is coupled with the driving circuit 140 and the dynamicfrequency adjustment unit 104, for temporarily storing image informationto be displayed. The driving circuit 140 is used for casting the imageinformation on the liquid crystal display panel 120. The control circuit160 is electrically connected with the dynamic frequency adjustment unit104 and the driving circuit 140.

It should be noted that in this embodiment, the driving circuit 140dynamically adopts different display refresh rates rather than a fixeddisplay refresh rate.

The method of dynamically selecting different display refresh rates isperformed by dynamically generating a display mode control signal by thedynamic frequency adjustment unit 104 based on an image characteristicclassification of the image information. Subsequently, the controlcircuit 160 accordingly adjusts the display refresh rate of the drivingcircuit 140 according to the display mode control signal.

The image characteristic classification of the above-mentioned imageinformation at least includes a dynamic image (such as a movie, ananimation and a moving image), a static slow image (such as ecologicalphotography and a page-turning advertisement), or a static holding image(such as an image, a photograph, a static print advertisement, andtexts). The dynamic frequency adjustment unit 104 can generates thecorresponding display mode control signal based on the imagecharacteristic classification of the image information.

For example, the dynamic image may be maintained at a high displayrefresh rate (such as 60 Hz); the static slow image may be switched to amedium display refresh rate (such as 20 Hz and 15 Hz); and the staticholding image may be switched to a low display refresh rate (such as 5Hz, 3 Hz and 0.3 Hz), but the invention is not limited to the case. Fora strong energy saving requirement, the dynamic image may also beswitched to a low display refresh rate.

As described above, in this embodiment, the dynamic frequency adjustmentunit 104 of the invention may have two sets (a high display refresh rateand a low display refresh rate), three sets (a high display refreshrate, a medium display refresh rate and a low display refresh rate) ormore of frame rates. In an embodiment, the dynamic frequency adjustmentunit at least has a frame rate lower than 20 Hz. In another embodiment,the dynamic frequency adjustment unit at least has a frame rate lowerthan 5 Hz. In yet another embodiment, the dynamic frequency adjustmentunit at least has a frame rate further lower than 1 Hz.

Moreover, the image information further has an image characteristicsub-classification. The image characteristic sub-classification at leastincludes a full color mode, an image mode or a text mode, and/or amonochromatic system. The dynamic frequency adjustment unit 104 cangenerate a corresponding display mode control signal based on the imagecharacteristic classification (the dynamic image, the static slow imageand the static holding image) and the image characteristicsub-classification (the full color mode, the image mode, the text modeand the monochromatic system) of the image information.

For example, the dynamic image, the static slow image and the staticholding image may be further divided into a full colormode/monochromatic system and a text/image mode. That is, thedynamic/static slow/static holding image may be further divided into atleast four sub-sortings, including a full color image, full color texts,a monochromatic image and monochromatic texts, but the invention is notlimited to the case.

Next, the display refresh rate may be adjusted based on differentsortings. Furthermore, other display configurations, such as a graylevel, may be further adjusted based on the image characteristicclassification and the image characteristic sub-classification.

For example, the dynamic image may be switched to the display refreshrate of 10 Hz-60 Hz and the gray level of 256; the static slow image ina full color mode may be further switched to the display refresh rate of3 Hz-10 Hz and the gray level of 64 or 256; the static slow image in atext mode may be further switched to the display refresh rate of 0.5Hz-3 Hz and the gray level of 4 or 16; and the static holding image inthe text mode and an energy saving mode may be further adjusted to thedisplay refresh rate of 0.05 Hz-0.5 Hz and the gray level of 2 or 4.

Furthermore, the dynamic frequency adjustment unit 104 first judges thedisplay mode of the image information, and subsequently performs a datareconciliation of the image information to be displayed. The examples ofthe data reconciliation are illustrated as follows.

We assume that the original data has a frame rate of 60 Hz, i.e. 60frames per second, then the original data has 600 frames per tenseconds, and the resolution is (Nx, Ny). Thus the data function may berepresented as Data(f, x, y, data(R,G,B)), f=1-600, x=1−Nx, y=1−Ny,wherein the data(R,G,B) is a RGB tristimulus value or a signal value (orrepresented as data(Y, x, y) or data(Y, u, v)).

Taking the frame rate of 10 Hz for comparison, every 6 frames areaveraged to obtain an average value Data10(6,x,y,data) to compare thefunction change and judge the mode thereof. That is, Data6(x, y,data)=(1/6)ΣData(f, x, y, data), f=1˜6, which represents that the sum ofevery 6 frame data is averaged.

Taking the frame rate of 5 Hz for comparison, every 12 frames areaveraged to obtain an average value Data12(x, y, data) for comparison.Taking the frame rate of 1 Hz for comparison, every 60 frames areaveraged to obtain an average value Data60(x, y, data) for comparison.Taking the frame rate of 0.5 Hz for comparison, every 120 frames areaveraged to obtain an average value Data120(x, y, data) for comparison.

Furthermore, in another embodiment, additionally within 10 seconds orother certain length of time, a mean square root (ΔData6, ΔData12,ΔData60 and ΔData600) of the above-mentioned Data6, Data12, Data60 andData600 is obtained for comparison. For example, ΔData6(x, y, data)={1/NΣ[Data6(x, y, data)−Data(f, x, y, data)]^2}^ 0.5. The mode is judged bythe operations above, and this statistical method facilitates improvingthe stability of judgment.

Furthermore, if the amount of data for computation is too large, thenumber of samples and gray scale may be reduced (for example, onlytaking the high level portion) for judgment.

Referring to FIG. 2, FIG. 2 illustrates a schematic circuit diagram ofthe liquid crystal display apparatus 100, but the hardware elementsincluded in the liquid crystal display apparatus 100 is not limited toFIG. 1. As shown in FIG. 2, the liquid crystal display apparatus 100also includes other electronic elements required for displaying, such asa timing control circuit, a low voltage differential signaling (LVDS)receiving circuit, an extended display identification data (EDID) unitand the like.

Referring to FIG. 3, FIG. 3 illustrates a schematic top view of a pixelunit 122 of the liquid crystal display apparatus 100. It should be notedthat the liquid crystal display panel 120 includes a plurality of pixelunits 122 (such as 1024*768 pixel units 122), a plurality of pixeldriving circuits 141, and each pixel unit includes a liquid crystalcapacitor Clc. The pixel driving circuit 141 includes a plurality ofstorage capacitors Cst, and the storage capacitors Cst respectivelycorrespond to the liquid crystal capacitors Clc. Each of the pixeldriving circuits 141 is controlled by the driving circuit 140 (as shownin FIG. 1 and FIG. 2). In general, the voltage level of the liquidcrystal capacitor Clc represents the content of the display signal. Thestorage capacitor Cst and the liquid crystal capacitor Clc are connectedin parallel. The storage capacitor Cst is mainly used for maintainingthe voltage level of the display signal. The refresh cycle of theabove-mentioned capacitor increases when the display refresh ratedecreases, which may cause decreasing of voltage retention rate,resulting in display distortion. However, in the invention, thecapacitance of the storage capacitors Cst far exceeds that of the liquidcrystal capacitors Clc, so as to improve the voltage retention rate ofthe display signal. In an embodiment, the capacitance of the storagecapacitors Cst is larger than or equal to ten times of, or even fiftytimes of that of the liquid crystal capacitors Clc. Thus, the voltageretention rate of the display signal is improved.

Referring to FIG. 4, FIG. 4 illustrates a schematic sectional view ofthe liquid crystal display panel 120 and the pixel driving circuit 141of the liquid crystal display apparatus 100. FIG. 4 is a schematic viewof a reflective TFT pixel, a transflective TFT pixel or a partiallyreflective TFT pixel, or a TFT pixel with high aperture rate (top ITO).Each pixel unit includes a gate layer and a first metal layer M1 (acommon electrode layer), a second metal layer M2 (a drain layer and anextension layer of the drain layer), and a third metal layer or pixelelectrode layer M3 (the pixel electrode layer is a reflective layer, ora partially transmissive and partially reflective layer, or atransparent electrode ITO layer) sequentially disposed on a lowersubstrate. Dielectric layer materials 11 and 12 may be respectivelydisposed between M1 and M2, and between M2 and M3. The liquid crystalcapacitor Clc is formed between the common transparent electrode layer(such as the ITO and IZO transparent electrodes) of the upper substrate(i.e., the filter substrate CF in FIG. 4) and the pixel electrode layerM3. On the lower substrate, the storage capacitor Cst is disposedbetween the common electrode layer M1 and the extension layer M2 of thedrain layer, and between the common electrode layer M1 and the pixelelectrode layer M3. In a practical application, the upper substrate maybe a color filter substrate.

Furthermore, in the transmissive liquid crystal display panel, thetransflective liquid crystal display panel, or the partially reflectiveliquid crystal display panel, each layer of M1, M2 and M3 may partiallyadopts (especially for the display area) a transparent ITO or IZOelectrode layer to increase the aperture rate, and the materials are notlimited to nontransparent metal materials.

The distance between the conducting materials (the common electrodelayer M1 and the extension layer M2 of the drain layer of the lowersubstrate) which form the storage capacitor Cst may be designed farsmaller than that of the conducting materials (the common electrodelayer of the upper substrate and the pixel electrode layer M3) whichform the liquid crystal capacitor Clc, so that the smaller distancebetween the conducting materials which form the storage capacitor Cst isused for improving the capacitance of the storage capacitor Cst.Furthermore, referring to FIG. 5, the planar extension area of thestorage capacitor Cst may also be used for improving the capacitance ofthe storage capacitor Cst. FIG. 5 illustrates a schematic view of thestorage capacitor Cst of the pixel unit 122. In an embodiment, the arearatio of the storage capacitor Cst to the pixel unit 122 is larger thanor equal to 85% (as shown in FIG. 5). In this regard, the capacitance ofthe storage capacitors Cst is larger than or equal to ten times of, oreven fifty times of that of the liquid crystal capacitors Clc. Thus, thevoltage retention rate of the display signal is improved.

In an embodiment, the average capacitance of the liquid crystalcapacitors Clc is larger than or equal to 0.5 picofarad. A liquidcrystal impedance of the liquid crystal display panel is larger than orequal to 10¹³ ohm/cm, and an alignment-film impedance of the liquidcrystal display panel is larger than or equal to ten times of the liquidcrystal impedance. In another embodiment, an alignment-film impedance ofthe liquid crystal display panel is further larger than or equal tofifty times of the liquid crystal impedance.

Moreover, in this embodiment, the pixel driving circuit 141 of theinvention may further adopts the dual-gate architecture 142 (referringto FIGS. 3 and 4).

The dual-gate architecture 142 can reduce the leakage current of thepixel driving circuit 141, which facilitates improving the voltageretention rate of the display signal. In an embodiment, an off-stateleakage current of the pixel driving circuit 141 may be less than orequal to 10-13 ampere. In another embodiment, the off-state leakagecurrent of the pixel driving circuit 141 may be further less than orequal to 10-14 ampere.

The detailed implementations of the dual-gate architecture 142 are shownin FIG. 6, which illustrates a schematic view of the dual-gatearchitecture 142. As shown in FIG. 6, the dual-gate architecture 142 ofthe pixel driving circuit 141 includes a lightly doped drain (LDD) TFT.The lightly doped drain

(LDD) TFT at least includes a first lightly doped drain LDD1 and asecond lightly doped drain LDD2 with different lengths, and the firstlightly doped drain LDD1 nearest to the driving transistor has thelargest length. The lightly doped drain (LDD) TFT is a dual-gate TFT, atleast including a first gate G1 and a second gate G2. The dual-gate thinfilm transistor (TFT) further includes a third lightly doped drain LDD3and a fourth lightly doped drain LDD4. The first gate G1 corresponds tothe first lightly doped drain LDD1 and the second lightly doped drainLDD2, and the second gate G2 corresponds to the third lightly dopeddrain LDD3 and the fourth lightly doped drain LDD4. The first lightlydoped drain LDD1 is nearest to the driving transistor and the firstlightly doped drain LDD1 has a length larger than that of the otherthree lightly doped drains (LDD2-LDD4).

Referring to FIG. 7, FIG. 7 illustrates a schematic view of anotherdual-gate architecture 142′. As shown in FIG. 7, the dual-gatearchitecture 142′ includes a substrate, an active layer, a first gateinsulating layer, a second gate insulating layer, a first gate layer anda second gate layer. The active layer is formed on the substrate. Thefirst gate insulating layer is formed on the active layer and covers afirst channel area, the fourth lightly doped area and the second lightlydoped area. The second gate insulating layer is formed on the activelayer and covers a second channel area, the third lightly doped area andthe fifth lightly doped area. The first gate layer is formed on thefirst gate insulating layer and covers the first gate insulating layerabove the first channel area. The second gate layer is formed on thesecond gate insulating layer and covers the gate insulating layer abovethe second channel area. The detailed descriptions and method forforming various dual-gate architectures are well known to those skilledin the art, and are not described herein.

As described above, the pixel driving circuit 141 of the invention mayfurther adopts various dual-gate architectures or multi-gatearchitectures, which reduce the leakage current of the pixel drivingcircuit 141, thereby improving the voltage retention rate of the displaysignal. As such, even when the display refresh rate of the liquidcrystal display apparatus 100 decreases, a good display effect may bestill maintained.

In an embodiment, the driving circuit 140 of the liquid crystal displayapparatus 100 further includes a row inversion method and a frameinversion method.

In the paragraphs mentioned above, the invention discloses a liquidcrystal display apparatus 100 having the dynamic adjustable refreshrate. The liquid crystal display apparatus 100 can accordingly adjustthe display refresh rate of the driving circuit based on an imagecharacteristic classification (such as a dynamic state, a static state,images, texts, fast changing and slow changing) of the currentlydisplayed image information, thereby achieving the power saving effectby adopting a dynamic switchable and low display refresh rate.Furthermore, the invention further provides a driving circuit having thedual-gate architecture for improving the capacitance of the storagecapacitor Cst and improving the voltage retention rate of the displaysignal at a low display refresh rate.

Referring to FIG. 8, FIG. 8 illustrates a schematic top view of a pixelunit 322 of a liquid crystal display apparatus according to a secondspecific embodiment of the invention. The design of the pixel unit ofthe second specific embodiment has characteristics of low leakagecurrent and a high voltage retention rate. The design of the pixel unitof the second specific embodiment may be used to support the liquidcrystal display apparatus 100 of the first specific embodiment havingthe dynamic adjustable rate, and maintain a stable display effect evenat a low display rate.

The liquid crystal display apparatus of the second specific embodimentincludes a liquid crystal display panel. The liquid crystal displaypanel at least includes a plurality of liquid crystal capacitors, aplurality of pixel units 322 (as shown in FIG. 8), an upper alignmentfilm layer and a lower alignment film layer. The liquid crystalimpedance is larger than or equal to 10¹³ ohm/cm, and the alignment-filmimpedance of the liquid crystal display panel is larger than or equal toten times of the liquid crystal impedance.

The driving circuit at least includes a display refresh rate and aplurality of storage capacitors. The storage capacitors respectivelycorrespond to the liquid crystal capacitors. The capacitance of thestorage capacitors is larger than or equal to ten times of that of theliquid crystal capacitors. The driving circuit casts the imageinformation on the liquid crystal display panel. The driving circuitcomprises two or more TFT switches, a dual-gate TFT or a LDD TFTcorresponding to each pixel element, and an off-state leakage current ofthe driving circuit is less than or equal to 10⁻¹² ampere. Otherdetailed descriptions of the liquid crystal display apparatus may bereferred to the illustrations of the first specific embodiment.

Referring to FIG. 9, FIG. 9 illustrates a schematic sectional view ofthe pixel unit 322 according to the second specific embodiment of theinvention. It should be noted that, as shown in FIGS. 8 and 9, the pixelunit 322 includes a first electrode layer M1, a second electrode layerM2 and a third electrode layer M3 disposed on the lower substrate. Adielectric layer material 11 is disposed between the first electrodelayer M1 and the second electrode layer M2, and a dielectric layermaterial 12 is disposed between the second electrode layer M2 and thethird electrode layer M3.

As shown in FIGS. 8 and 9, the second electrode layer M2 includes anextension layer of a drain layer. The third electrode layer M3 includesa pixel electrode layer. A dielectric layer material is respectivelydisposed between the first electrode layer and the second electrodelayer, and between the second electrode layer and the third electrodelayer. The first electrode layer M1 includes a gate layer 342 and/or acommon electrode conductive layer 324 (as shown in FIG. 8). Theextension layer of the drain layer is connected with the pixel electrodelayer, and/or the common electrode conductive layer 324 is electricallyconnected with a common transparent electrode layer of the uppersubstrate. The liquid crystal capacitor is formed between the commontransparent electrode layer of the upper substrate and the pixelelectrode layer of the lower substrate. The storage capacitor may havethree parts. The first part, storage capacitor Cst1, is disposed betweenthe common electrode conductive layer 324 of the first electrode layerM1 and the extension layer of the second electrode layer. The secondpart, storage capacitor Cst2, is disposed between the common electrodeconductive layer of the first electrode layer M1 and the pixel electrodelayer of the third electrode layer M3. The third part, storage capacitorCst3, is disposed between the gate layer of the first electrode layer M1and the pixel electrode layer of the third electrode layer M3.

In the design of the pixel unit 322 mentioned above, the pixel electrodelayer is a transparent electrode, a metal reflective electrode or acombination thereof. The liquid crystal display panel may be atransmissive liquid crystal display panel, a reflective liquid crystaldisplay panel, a transflective liquid crystal display panel or apartially reflective liquid crystal display panel. The dielectric layermaterial of the storage capacitor is a silica material SiOx, a nitrogenoxide material SiNx, a resin material, a plastic material or aphotoresist material. The dielectric layer material of the storagecapacitor has a thickness less than or equal to 0.2 μm. In the pixelunit 322 of the above-mentioned embodiment, the pixel electrode layer isof a pixel electrode layer architecture including Indium Tin Oxide (ITO)slits. Referring to FIG. 14, FIG. 14 illustrates a schematic view of apixel electrode layer including ITO slits. As shown in FIG. 14, severalslits are disposed on the common electrode layer ITO of the pixel unit322. The liquid crystal layer is constructed by negative liquid crystalsaligned vertically.

Furthermore, in another embodiment, another pixel unit design of theinvention is as follows. Each pixel unit at least corresponds to one ofthe liquid crystal capacitors and one of the storage capacitors. Eachpixel unit includes the gate layer of the first electrode layer M1, thesecond electrode layer M2 and the common electrode layer of the thirdelectrode layer M3 sequentially disposed on the lower substrate.Dielectric layer materials (11, 12) are respectively disposed betweenthe first electrode layer M1 and the second electrode layer M2, andbetween the second electrode layer M2 and the third electrode layer M3,as shown in FIGS. 8 and 9.

It should be pointed out that the second electrode layer M2 includes asource layer, a drain layer and a pixel electrode layer connected withthe drain layer. The pixel electrode layer of the second electrode layerM2 and the common electrode layer of the third electrode layer M3 areformed in a comb-shaped electrode architecture, a grid-shaped electrodearchitecture, a curving comb-shaped electrode architecture or a curvinggrid-shaped electrode architecture. No common electrode layer isdisposed on the upper substrate. A color filter and a flat layer may bedisposed on the upper substrate. The liquid crystal capacitor is formedin the curving electric field between the pixel electrode layer of thesecond electrode layer and the common electrode layer of the thirdelectrode layer. The storage capacitor is disposed between the pixelelectrode layer of the second electrode layer and the common electrodelayer of the third electrode layer.

Referring to FIGS. 10 and 11, in an embodiment, the pixel electrodelayer in FIGS. 10 and 11 is of an in plane switching architecture. Theliquid crystal molecular layer can be formed by liquid crystals(positive or negative liquid crystals) aligned horizontally. The pixelelectrode layer and the common electrode layer are metal or alloyconductive electrodes. The pixel electrode layer and the commonelectrode layer of the lower substrate of the liquid crystal displayapparatus are comb-shaped or grid-shaped electrodes, or curvingcomb-shaped or grid-shaped electrodes.

In another embodiment, the liquid crystal display apparatus of the inplane switching architecture at least includes a pixel electrode layerand a common electrode layer. The pixel electrode layer and the commonelectrode layer may are of a comb-shaped or grid-shaped electrodearchitecture, or a curving comb-shaped or grid-shaped electrodearchitecture. The common electrode layer is a first metal electrode M1,and the pixel electrode layer is a second metal electrode M2. Thestorage capacitor formed by the M1 and M2 may be located at the positionof the comb-shaped or grid-shaped electrodes, and even a circle (orsquare-shaped) storage capacitor is formed.

In yet another embodiment, referring to FIGS. 12 and 13, the pixelelectrode layer may also be of the fringe field switching architecture.The liquid crystal molecular layer may be constructed by negative liquidcrystals aligned horizontally. The pixel electrode layer and the commonelectrode layer are ITO or IZO transparent electrodes, or metal or alloyconductive electrodes. In this embodiment, the pixel electrode layer maybe a rectangle or unit-pixel electrode layer. The common electrode layermay be a comb-shaped or grid-shaped electrode, or a curving comb-shapedor grid-shaped electrode (as shown in FIG. 12).

In the design of the pixel unit mentioned above, the pixel electrodelayer may also be a transparent electrode, a metal reflective electrodeor a combination thereof. The liquid crystal display panel may be atransmissive liquid crystal display panel, a reflective liquid crystaldisplay panel, a transflective liquid crystal display panel or apartially reflective liquid crystal display panel. The dielectric layermaterial of the storage capacitor is a silica material SiOx, a nitrogenoxide material SiNx, a resin material, a plastic material or aphotoresist material. The dielectric layer material of the storagecapacitor has a thickness less than or equal to 0.2 μm. In view of theabove, the pixel design and the liquid crystal material of various pixelunits disclosed in the second specific embodiment may be used forsupporting to dynamically adjust the liquid crystal display apparatus toa low display refresh rate, thereby reducing the energy cost of theliquid crystal display apparatus. Thus, by using the method of theinvention, a liquid crystal display apparatus with high energyefficiency and a stable display effect (abnormal display conditions suchas screen scintillation may be avoided) is provided.

Furthermore, the invention may be further applied in a liquid crystaldisplay apparatus having brightness or luminance holding ratiocompensation. The transmittance of the liquid crystal display panelincreases with time in a display frame cycle. The backlight module canform a plurality of backlight shield-blocking periods in a display framecycle, or gradually adjust the backlight driving current.

Although the invention has been disclosed with reference to the aboveembodiments, these embodiments are not intended to limit the invention.It will be apparent to those of skills in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention. Therefore, the scope of the inventionshall be defined by the appended claims.

What is claimed is:
 1. A liquid crystal display apparatus, comprising: aregister for temporarily storing image information; a liquid crystaldisplay panel comprising a plurality of liquid crystal capacitors, aplurality of pixel units, an upper alignment film layer and a loweralignment film layer; a driving circuit comprising a plurality ofstorage capacitors corresponding to the liquid crystal capacitors,wherein a capacitance of the storage capacitors far exceeds acapacitance of the liquid crystal capacitors, and the driving circuitcasts the image information on the liquid crystal display panel; adynamic frequency adjustment unit for computing and judging based on animage characteristic classification of the image information stored inthe register and dynamically generating a display mode control signal;and a control circuit electrically connected with the dynamic frequencyadjustment unit and the driving circuit, wherein the control circuitadjusts a display refresh rate and a display configuration of thedriving circuit according to the display mode control signal, whereineach of the plurality of pixel units of the liquid crystal display panelat least corresponds to one of the liquid crystal capacitors and one ofthe storage capacitors, each pixel unit comprises a first electrodelayer, a second electrode layer and a third electrode layer sequentiallydisposed on a lower substrate, the second electrode layer comprises anextension layer of a drain layer, the third electrode layer comprises apixel electrode layer, dielectric layer materials are respectivelydisposed between the first electrode layer and the second electrodelayer, and between the second electrode layer and the third electrodelayer, the first electrode layer comprises a gate layer and/or a commonelectrode conductive layer, and the extension layer of the drain layeris connected with the pixel electrode layer, and/or the common electrodeconductive layer is electrically connected with a common transparentelectrode layer of a upper substrate, wherein the liquid crystalcapacitor is formed between the common transparent electrode layer andthe pixel electrode layer of the lower substrate, and the storagecapacitor is disposed between the common electrode conductive layer ofthe first electrode layer and the extension layer of the secondelectrode layer, and/or between the common electrode conductive layer ofthe first electrode layer and the pixel electrode layer, and/or betweenthe gate layer of the first electrode layer and the pixel electrodelayer.
 2. The liquid crystal display apparatus of claim 1, wherein theimage characteristic classification comprises a dynamic image, a staticslow image or a static holding image, the display configurationcomprises a gray level depth.
 3. The liquid crystal display apparatus ofclaim 2, wherein the image information further has an imagecharacteristic sub-classification, which comprises a full color mode, animage mode, a text mode, a monochromatic image mode and/or a low graylevels mode, and the dynamic frequency adjustment unit generates acorresponding display mode control signal based on the imagecharacteristic classification and the image characteristicsub-classification of the image information.
 4. The liquid crystaldisplay apparatus of claim 1, wherein the dynamic frequency adjustmentunit at least has two or more sets of display frame rates.
 5. The liquidcrystal display apparatus of claim 1, wherein the driving circuitcomprises two or more thin film transistor (TFT) switches, a dual-gatethin film transistor or a lightly doped drain (LDD) thin film transistorcorresponding to each pixel unit, and an off-state leakage current ofthe driving circuit is less than or equal to 10⁻¹² ampere, the LDD TFTof the driving circuit at least has a first lightly doped drain and asecond lightly doped drain with different lengths, and the first lightlydoped drain nearest to the driving transistor has the largest length.